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Request for lab ideas

David R. Hershey dh321 at PGSTUMAIL.PG.CC.MD.US
Wed Dec 13 21:34:07 EST 1995


Hydroponics (solution culture) is a relevant (space station,
commercial, and research uses, Epcot Center tourist attraction)
and intriguing lab experiment, although the standard deficiency
experiment takes a minimum of about 3 weeks to obtain good
symptoms. It also has the advantage of allowing students to see
the entire plant, roots and all, which clearly demonstrates that
plants do not need soil. Many types of hydroponic experiments are
possible: aeration effects, plant effects on nutrient solution
pH, toxicity symptoms, salinity effects, hydroponics versus
geoponics (soil culture), ammonium versus nitrate as the nitrogen
source, and symbiotic nitrogen fixation. Some of these are
detailed in my book, Plant Biology Science Projects (1995, John
Wiley & Sons). 

Unlike most lab manuals, which use sunflower, tomato, bean, or
corn, I prefer houseplants, like piggyback plant (Tolmiea
menziesii), a Pacific Northwest native. It is excellent for
hydroponic experiments because it is easily clonally propagated
by rooting adventitious foliar plantlets directly in solution, it
requires no staking, it is tolerant of low light, and it readily
develops iron deficiency symptoms. Tolmiea roots can even be
coated with red iron oxide and still develop iron deficiency when
grown hydroponically without a chelate and without ammonium
nitrogen. Wandering jew (Tradescantia or Zebrina species) is a
good monocot houseplant for hydroponics. 

Many dwarf bedding plants can be raised from seed hydroponically
in 35-mm plastic film cans under continuous fluorescent light. No
aeration is used but the film can is only filled about half full
so the roots receive adequate oxygen. I have had dwarf marigolds
in flower 6 weeks after sowing. Other plants I have had success
with are zinnia 'Thumbelina', coleus, impatiens, celosia 'Jewel
Box', and polka dot plant (Hypoestes phyllostachya).

Consumer experiments that compare plant growth with different
brands of potting soils, fertilizers, and similar products can
generate student interest. Comparing a standard nutrient solution
to a houseplant fertilizer, such as Miracle-Gro, will
dramatically reveal that it is far from miraculous in
hydroponics. I have a collection of houseplant fertilizers with
the price of nitrogen ranging from less than $31 to $4660 per kg
of nitrogen, yet they all work about the same if you dilute them
properly.

Cut flowers are good subjects for lab experiments. Carnations can
be dyed to visually demonstrate water movement in the xylem. Try
your school's colors for homecoming or green for St. Patrick's
day. Investigate the effect of recutting a flower stem underwater
on vase life or compare the benefits of commercial flower
preservatives to traditional treatments, like sugar, aspirin, or
a copper penny. Carnation vase life is doubled or tripled by
treating with silver thiosulfate because silver blocks ethylene
action. 

Devil's backbone (Kalanchoe daigremontiana), a CAM plant from
Madagascar, is another houseplant that can be used for many
student experiments. It produces numerous adventitious plantlets
on the edges of its leaves. The plantlets are easily rooted by
floating them on water and used in hydroponics or for other
experiments. Adventitious plantlet formation is under
photoperiodic control (long day response) in the intact plant but
not in detached leaves.

Having students experiment with plants that they can take home as
houseplants often seems to generate interest. Also, relatively
few houseplants have been the subject of much research, so class
experiments can make original observations of nutrient deficiency
symptoms and other responses.

Giving students a houseplant at the start of the semester to take
home and assigning them to keep track of its growth, its
environment, and the care they give it usually generates some
excellent reports. 


******************************************************************
David R. Hershey
					
Snail mail:			Adjunct Professor
				Biology/Horticulture Department
6700 Belcrest Road #112		Prince George's Community College
Hyattsville, MD 20782-1398	Largo, MD 20772-2199

Email: dh321 at pgstumail.pg.cc.md.us
*******************************************************************





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